Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Jun. 30, 2015 USD ($) fund	Dec. 31, 2014 USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	$ 390.1	$ 407.0
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments | fund	14
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments | fund	29
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Largest single fund investment	$ 25.0